When should the information system owner document the information system and authorization boundary description in the security plan? Response:

Documenting the system and boundary after control implementation is too late, as the boundary and system description inform the selection and implementation of those controls.

While assembling the authorization package is when the security plan is finalized, the initial documentation of the system and boundary needs to occur earlier, specifically after categorization.

After security categorization, the system's impact level (low, moderate, high) is determined, which is foundational for defining the scope, authorization boundary, and ultimately the appropriate security controls, thus requiring system and boundary documentation at this stage in the security plan.

Reviewing the security control assessment plan happens much later in the process, after the system and boundary have already been defined and controls implemented.